This invention relates to a developer for developing electrostatic latent images in electrophotography, electrostatic recording, electrostatic printing and the like.
In electrophotography etc., electrostatic latent images are developed normally or reversely to make them visible by a cascade developing method (U.S. Pat. Nos. 2,297,691, 2,618,552), a magnetic blush developing method (U.S. Pat. No. 2,832,311), (both methods use a developer of mixture of a toner with a carrier), or by a touch down developing method (U.S. Pat. No. 4,121,931) wherein a developer is composed only of a toner, or by a nonmagnetic single component developing method (U.S. Pat. No. 3,731,146), and thereby stable copied images of high quality are obtained.
In general, a toner suitable for developing methods aforementioned is the one that is prepared by mixing a thermoplastic resin as a binder resin with a colorant such as a dye or a pigment, a positive or negative charge-controlling agent or a surface lubricant such as a wax, followed by kneading, grounding and classifying to obtain toner particles of 5-20 .mu.m in mean particle size.
A charge controlling agent that charges a toner positively is disclosed, for example, in U.S. Pat. Nos. 4,338,390, 4,490,455, 4,493,883, or 4,415,646.
A charge controlling agent that charges a toner negatively is disclosed, for example, in U.S. Pat. Nos. 4,206,064, 4,656,112, 4,665,001.
However, when these toners per se known are used singly, there are such problems as unstability of chargeability of toners, electrification-build-up properties and uniformity of charged amount because of poor dispersion of charge controlling agents in toners.
It is known that chargeability of toner is controlled by using a resin having a polar group suitable for positive charging, for example, in U.S. Pat. Nos. 4,371,601, 4,504,563 or 4,686,166. These resins per se known, however, have amino groups, and so there are such problems as charging stability and electrification-build-up properties under highly humid environment.
On the other hand, it is known that a resin having a polar group suitable for negative charging is used for controlling chargeability of toner, for example, in U.S. Pat. No. 3,998,747. These resins per se known, however, show such problems as charging stability and electrification-build-up properties in spite of the presence of a halogen group, or oxygen group.
It is known that inorganic fine particles are used as charge giving materials. Japanese Patent Laid Open Nos. 135739/1977, 123550/1981 disclose that metal oxide powders treated with amino-silane can give strong positive chargeability. But, because aminosilane is hydrophilic, there arise such problems as toner flow characteristics and charge variation with time under high temperature and high humidity. There is also known a toner containing metal oxide treated with aminosilane and a hydrophobic agent in Japanese Patent Laid-Open Nos. 216252/1983, 73271/1988, 73272/1988. There also arise such problems as toner flow characteristics, electrification-build-up properties and charging stability.
It is known that controlling agents for positive charging are absorbed on hydrophobic silica fine particles in, for example, Japanese Patent Laid-Open Nos. 135855/1980, 80651/1983. There also arise such problems as toner flow characteristics, electrification-build-up properties and charging stability.
Japanese Patent Publication No. 20344/1979 discloses a negatively chargeable toner containing hydrophobic silica fine particles. Hydroxy groups on the surface of silica particles are, for example, replaced by hydrophobic groups such as a methyl group and the like. Such silica as thus prepared can be charged negatively, but there also arises such a problem as unsatisfactory electrificaition-build-up properties etc.
Japanese Patent Publication No. 93455/1985 is to improve a negative charging level of a toner by utilizing charging properties of polar groups present on the surface of inorganic fine particles, which are surface-treated with fluorine-substituted silane coupling agent having polar groups suitable for negative charging. It is sure that such a toner has been improved in charging level, but flow characteristics of a toner, electrification-build-up properties and charging stability are insufficient.
Conventional toners can not solve such problems as flow characteristics of toner, dirts of copied images caused by toner flying, dirts inside a machine, fogs on a copying ground, fogs like memorized images and voids in copied images or the like in a high-speed copying machine desired recently, a color-copying machine, an electrophotographic printer or a non-magnetic single component developing machine.
Further, Japanese Patent Laid-Open No. 135854/1980 discloses that controlling agents for negative charging are absorbed on silica fine particles. But, there are such problems as toner flow characteristics, electrification-build-up properties and charging stability.